POC - Restructure video processing and add gpx, nmea and exiftool runtime support

[malconsei]

This PR is a proof of concept covering video processing (process command applied to videos)

Restructuring:

• Extract common logic for track handling
• Consider all track sources the same

New features:

• Support GPX and NMEA tracks for videos
• Support invoking exiftool internally
• Support chaining multiple parsers and/or the same parser with different options
• Support defining filename patterns for data sources based on the original video filename
  • %f: full video filename
  • %g: video filename without extension
  • %e: video extension (inclusive of .)

Examples:

# short format
python -m mapillary_tools.commands --verbose  process --video_geotag_source exiftool_runtime  videos/insta360/

# long format - with options
python -m mapillary_tools.commands --verbose  process --video_geotag_source {"source": "exiftool_xml", "pattern": "../%g.insv.xml"}  videos/insta360/converted/

# multiple sources
python -m mapillary_tools.commands --verbose  process --video_geotag_source {"source": "gpx", "pattern": "../%g.gpx"} --video_geotag_source {"source": "gpx", "pattern": "../%g.xml"}  videos/gopro/

TODO:

• Tests
• Fixes :P